Wilcock et al., 16 December 2016
Axial Seamount was chosen as a key site on the Regional Cabled Observatory because it is the most active volcano on the Juan de Fuca Ridge having erupted in 1998, 2011, and 2015 [1-7] and because it has a long history of observations as the site of the first submarine volcanic observatory “NeMO” [1-2; https://www.pmel.noaa.gov/eoi/nemo/index.html]. Axial is also unique because the structure of microbial communities has been examined for over 2 decades, including prior to and immediately following the eruptions [8-11]. Nearly continuous seafloor deformation measurements began in 1998 using battery-powered bottom pressure recorders (BPR’s), augmented by mobile pressure recorders in 2000 [3,12-14]. In 2014, an array of cabled bottom pressure tilt instruments, developed by Chadwick [13,14], were installed within the caldera providing real-time measurements of seafloor inflation caused by magma injection in the subsurface and extremely rapid deflation events coincident with eruptions and draining of the magma chamber [13,14]. In concert, these measurements, coupled with modeling, provide forecasting of when the next eruption may occur [13,14; https://www.pmel.noaa.gov/eoi/axial_blog.html].
The ability to make such forecasts is rare in both terrestrial and submarine environments, however, they are possible at Axial due to the continuous magma supply from the Cobb hotspot plume [12-14]. The subsurface structure of Axial is the best imaged submarine volcano due to multiple seismic imaging programs. In concert, these field programs have resulted in 3-D tomographic imaging of the magmatic system [15-20], providing unparalleled insights into melt distribution and magma flux, which controls seafloor deformation. Two large magma bodies at 1.1 to 2.6 km beneath the seafloor [15-18] and a newly recognized deep 3-5 km wide conduit located 6 km beneath the seafloor have been imaged . The conduit is interpreted to contain a series of stacked melt lenses (sills) with spacings of 300-450 meters, providing melt transport that activated the eruptions in 1998, 2011, and 2015 . The 22-year monitoring of Axial Seamount by Chadwick and Nooner document co-eruption deflation events in the caldera of 2.5-3.2 meters, followed by variable periods of inflation . Based on the long-term time series, the 2015 eruption was forecast within a 1-year time window, seven months in advance of the eruption . Daily updates are provided by the model, and coupled with real-time seismic measurements [e.g. 21], will allow refinement of when the next eruption will occur.
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